The invention relates to the field of medical devices, and more particularly to catheters, such as needle catheters or other elongated devices configured for inserting into a patient's body lumen or cavity to perform a diagnostic and/or therapeutic procedure.
An essential step in treating or diagnosing cardiac tissue or cardiovascular diseases using an interventional catheter is the proper placement of the catheter at a desired location within the patient, which consequently requires accurate imaging of the catheter location within the patient. Although various methods of imaging catheters within a patient are possible, ultrasonic imaging (also referred to as sonic, acoustic or echo imaging) would provide several advantages. For example, ultrasonic imaging is very safe for the expected extended imaging time periods required for catheter diagnostic and/or therapeutic guidance, unlike imaging methods which expose the patient to x-rays such as CT/EBCT (Electron Beam Computed Tomography) or bi-planar fluoroscopy. Additionally, ultrasound is relatively inexpensive compared to other imaging modalities such as MRI or CT/EBCT, and ultrasound can provide many of the functional diagnostics, such as cardiac wall motion and thickness information, which these expensive modalities provide.
However, one difficulty has been visualization anomalies, including artifacts, lack of an image of catheter sections, and overly bright and/or large images of other catheter sections, in the ultrasonic images of catheters. Such artifacts can provide a misleading and inaccurate impression of the shape and/or location of the catheter within the patient's anatomy. Catheter elements can appear so bright and large on the ultrasonic image (called “blooming”) due to their direct highly sonic reflective nature relative to the anatomy, especially at the gain settings typically used to image the anatomy, that the image of the adjacent anatomy is obscured by the catheter image. For example, metallic portions of catheters can produce strong/high amplitude direct echoes (bright images), and a ringing artifact in the form of a pyramid shape of reverberation (“ringing”) images on a three-dimensional ultrasonic imaging system, and a triangular shape of reverberation images on a two-dimensional ultrasonic imaging system, trailing off in the viewing direction. Similarly, most thermoplastic catheter shaft surfaces produce strong/high amplitude direct echoes formed by the reflection of sonic energy off a catheter material interface or surface perpendicular to the viewing direction and directly back to the ultrasonic transducer. If the gain settings of the ultrasonic imaging system are reduced to improve the image of the catheter shaft portions by reducing its image and artifact brightness, the image of the anatomy fades to the point of being significantly less visible or not visible at all. Additionally, given that most thermoplastic catheter shafts and their components are smooth (i.e., surfaces/material interfaces that behave as smooth surfaces at the ultrasonic frequencies of interest), the portions of the catheter shaft being imaged at oblique angles reflect the sonic energy away from the ultrasonic transducer and produce a very faint/small image or no image of the catheter shaft surface, which obviously is problematic. For example, locations in the displayed image where the catheter shaft produces no image may be falsely interpreted as the location of the distal end of the catheter and result in the improper or undesired positioning of the catheter. However, if the gain settings of the ultrasonic imaging system are increased to improve the image of these portions of the catheter shaft (increase its image brightness), the image of the anatomy, direct echo catheter surface/material interface images and any artifacts enlarge and brighten significantly, increasing the degree to which they obscure the image of the catheter shaft and the location of adjacent tissue surfaces. Therefore, it would be a significant advance to provide a catheter with improved imaging characteristics by two-dimensional and three-dimensional ultrasonic imaging systems for enhancing the ability to guide and visualize a catheter in the patient's anatomy during diagnostic and/or therapeutic procedures.